The present invention relates to a joined structure of a metal member, particularly metal terminal, and a ceramic member, and an adhesive material therefor.
Dense ceramics are noted as a base material for an electrostatic chuck. In the field of semiconductor producing systems, electrostatic chucks have been practically used as susceptors containing an electrode for applying high frequency power to generate plasma. In such a device for applying high frequency power, the electrode for applying high frequency power has been embedded in a substrate made of silicon nitride or alumina.
In such devices, it is necessary to embed a metal electrode in a ceramic substrate such as aluminum nitride, alumina or the like and to electrically connect the metal electrode to an outer connector for supplying electric power. The Applicants disclosed a process of producing a ceramic heater, an electrostatic chuck and an electrode system for applying high frequency voltage used for a semiconductor producing system (see Japanese Patent Laid-Open “Kokai” Numbers 277,173A/1996 and 209,255A/1998). In these applications, Applicants proposed the following process for producing a joined structure. A hole is formed in a ceramic substrate by machining to expose a part of a metal electrode that is embedded in the substrate. A metal terminal with the shape of a cylinder is inserted into the hole and its end face is adhered to the metal electrode by brazing.
The inventors have tried the following process for brazing a ceramic member and a metal terminal. In this process, a hollow or a blind hole is formed in a surface region of a ceramic member and the end face of a metal terminal is inserted into the hollow. A metal foil is interposed between the metal terminal and the inner wall surface of the ceramic member facing the hollow to obtain an assembly, which is then heated to join the terminal and member by brazing. In an actual production line, however, some problems were found in the step of cooling the ceramic member to room temperature after the brazing (heating) step. That is, cracks may occur in the ceramic member near the inner wall surface, particularly near the corner portions of the hollow of the ceramic member. Such cracks result in off-specification products and reduce the production yield.